View source for How RL78 manages named address spaces

RL78 contains 2 address spaces:

'''Near address space'''

- qualifier '''__near'''

- 16 bit addresses

- saved in the topmost 64 kB of the address space

'''Far address space'''

- qualifier '''__far'''

- 20 bit addresses


The default (generic) address space for the RL78 targets is the '''__near''' address space. For now there is no option available to make the '''__far''' address space the default one.

Below are a few examples of the way '''__far''' address space can be used:

Examples:

  __far char a, b, c;
  // Declares three characters in address space __far

  struct { int a; char b; } * __far q;
  // Declares a pointer in address space __far that points to a structure in the generic space (__near)

There are some constraints on the use of address-space type qualifiers:

Since address space '''__far''' encloses address space '''__near''', then every location (address) within '''__near''' is also within '''__far'''.

The most significant constraint is that an address space name cannot be used to qualify an object that has automatic storage duration. This implies, in particular, that variables declared inside a function cannot be allocated in a named address space unless they are also explicitly declared as '''static''' or '''extern'''.

  void X()
  {
  	__far char a;
  }
  //compilation errror

For the examples above, the declarations of a, b, c, and q would have to be outside any function to be valid.

As determined by its type, every pointer points into a specific address space, either the generic address space or a named address space. A pointer into an address space can only point to locations in that address space (including any subset address spaces).

Pointers into '''__far''' address spaces cannot be passed as arguments to library functions. Likewise, library functions such as '''malloc''' that allocate memory do so only for the generic address space ('''__near'''); there are no standard functions for allocating space in the '''__far''' address spaces.

More detailed information about named space addresses can be found [http://std.dkuug.dk/jtc1/sc22/wg14/www/docs/n1005.pdf here]